This invention relates generally to electrostatic sprayers and more particularly to an electrostatic spray module for agricultural applications.
Electrostatic sprayers are commonly used in agricultural applications to apply pesticides and other agricultural chemicals to crops. Electrostatic sprayers typically work based on the following basic principles. Compressed air and liquid (for agricultural applications this is typically a pesticide) are separately piped into a nozzle, where the two mix in the process of atomization, forming small droplets of the liquid. The atomized liquid then passes through a charged electrode, in the process of induction, which charges the droplets. The droplets then, due to the flow of air, spray out to the crops. The charge on the droplets causes the individual droplets to repel from each other scattering the spray for an even and wide spread application. The charge on the droplets also leads to better application by causing the droplets to better adhere to the crops, which are at ground potential and electrically attract the charged droplets.
To sufficiently charge the liquid in an electrostatic sprayer, the nozzle needs a high voltage power source of generally one kilo-volt or higher. Electrostatic sprayers designed for use in the field use a low voltage power supply, such as a 12 V battery (typically the tractor battery), that is hooked up to a power supply that generates a high voltage signal. Some sprayers use one power supply for many nozzles, but have the complications of distributing high voltage over several nozzles. Many sprayers use one power supply per nozzle to keep the high voltage local to the nozzle but have the disadvantage of the high cost and maintenance of the many power supplies.
Systems incorporating individual electrostatic nozzles modules tend to be systems that are cumbersome to hook-up, difficult to configure, hard to maintain, have limitations in their performance and are costly to manufacture.
A "sprayer" in agricultural parlance refers to a electrostatic spray nozzle system or module as well as the supporting components of an air compressor, a liquid tank and pump, a frame and a boom, all of which are typically mounted on a tractor.
A standard sprayer typically comprises 30 to 80 nozzles each with several hoses and connections. Each nozzle in the sprayer requires a hose leading from the compressed air source, a hose leading from the liquid source and either a low voltage or high voltage power supply connection. Multiplying these three connections over the dozens of nozzles that are typically hooked to a tractor boom and the result is a cumbersome process for hooking up a sprayer system. This process can take considerable labor resources and result in a system that is extremely difficult to maintain.
Traditional sprayer systems also tend to have a fixed configuration, making changes to such things as the size of the nozzle opening and the spacing of the nozzles difficult, if not impossible, to alter after manufacturing. Changing the size of the opening in a nozzle affects the airflow through the nozzle, resulting in either lower airflow through the nozzle or a higher pressure. Varying the size of the nozzle opening may be desirable based on the type or stage of a crop. For example, a vineyard in springtime will consist of small plants where it will be preferable to use less air volume or pressure than later in the season when the plants are larger. Changing the spacing of the nozzles can also be difficult in prior art sprayer systems. A fixed distance between nozzles may not be desirable as different crops and different conditions have different nozzle requirements. For example, a sprayer used at a golf course will want full coverage over a flat surface, which will optimally be a nozzle every four inches or so. Meanwhile, a cotton crop has rows spaced such that a nozzle every twelve inches would provide adequate coverage.
Prior art sprayer systems are also difficult to maintain. The prior art nozzle described in Cooper et al., U.S. Pat. No. 5,704,554, shown in FIG. 1, has components, such as the electrode 2 and the liquid channels 5 integrated into the nozzle. Parts such as these may need routine cleaning for optimal use of the nozzle. Build up of dirt and liquid on the electrode can lead to inefficient spraying and excessive current draw on the power supply. Cleaning of the embedded electrode is awkward and can lead to damaging the surface of the electrode and the plastic enclosing the electrode. Cleaning the non-removable liquid channel is difficult. The tip of the liquid channel is subject to build-up of conductive deposits that create electrical current pathways and can lead to carbon deposits building up on the liquid channel tip. Excessive build up can damage the tip of the liquid channel, resulting in an inoperable nozzle. Excessive damage to the electrode or the liquid channel in a nozzle where such parts are non-replaceable requires complete replacement of the full nozzle.
Prior art sprayer systems also have performance limitations. The thin electrode 2 shown in the prior art nozzle of Cooper, et al., in FIG. 1 only provides a limited charge to the droplets, not fully maximizing their ability to attract to crops. Many prior art nozzles also have problems with the flow of the atomized liquid through the tip of the nozzle. This is caused by imperfections in the inner orifice wall of the tip of the nozzle. For example, the prior art nozzle of FIG. 1 has a stainless-steel electrode 2 embedded between plastic 1 and ceramic 3 layers, resulting in a three-layered passage from the end of the liquid channel 5 to the opening after the electrode 6. This three-layered channel of dissimilar materials, even with quality machining, has microscopic notches between the layers of materials. These notches magnify with wear and tear on the nozzle and the wear and tear, in turn, is accelerated by the damaging effects caused by the notching. As the air and liquid mixture flows out of the channel, the mixture eddies along the notches resulting in decreased charging of the spray, increased current draw and physical deterioration of the inner surface of the nozzle. The notching and the dissimilar materials can cause the liquid to be deflected to the side in its passage through the nozzle, causing an inefficient spray pattern and sub-optimal charging by the electrode. Another performance limitation in some prior art nozzles is an off-center spray, resulting from liquid channels that are not in complete coaxial alignment with the output of the nozzle. FIG. 1 shows a prior art nozzle that has a liquid channel with one end of the liquid channel centered about the electrode, but not the entire channel at the end is not straight upstream from the opening. An off-center liquid channel can result in a spray that is not centered around the end of the nozzle due to a lateral force in the liquid generated in the liquid's passage through the off-center liquid channel 5. Further, this can lead to plugging of the nozzle. Prior art nozzles also passively rely on the liquid maintaining ground potential which leads to unreliable charging of the spray.
Lastly, prior art sprayer systems are expensive. Due to the high cost of sprayer systems, their use is generally limited to high-value cash crops and specialty applications such as vineyards. The expense of prior art sprayer systems limits their use in commodity crops.
Therefore, there is a need for a system for electrostatically spraying agricultural crops that is easy for a user to set up, convenient to configure to different field situations and simple to maintain. Further, there is a room for improvement in the performance of sprayer systems as well as a strong need for more affordable systems.